Pumping fluids from deep wells presents unique challenges as space limitations are severe and head pressures may be extreme. Oil wells are known to exceed three thousand meters in depth, and water wells exceeding three hundred meters are not extraordinary. Among the most common pumps currently in use in deep well applications are single acting reciprocating piston pumps. These pumps are generally used in conjunction with pump jacks in oil and water wells and are comprised of one or more pistons in a cylindrical pump barrel submerged beneath the static fluid level. A steel discharge conduit, coaxial with the casing and typically at least five centimeters in diameter, is typically be used between the pump barrel and the well head to secure the pump barrel in a fixed position down hole.
The pistons are operated by a rigid rod reciprocating within the discharge conduit and connected to a prime mover at the well head. The ordinary reciprocating rod pump operates on a direct linkage with the piston(s) recharging on the down stroke and discharging on the up stroke causing an imbalanced power demand on the prime mover and often occasioning the need for counterbalancing. The requisite steel discharge pipe anchoring the pump barrel must be of a bore adequate to accept the rod and pistons to allow servicing multiple piston washers without removal of the discharge pipe. At extreme depths, hydraulic friction within the discharge pipe may impede pumping efficiency over what would otherwise be available in the surrounding larger diameter casing, particularly when pumping viscous oil. The capital cost of this type of system, including drilling a large bore hole, then providing large diameter casing a coaxial steel discharge pipe string, pump and drive rod is considerable. When pump barrel or foot valve repairs oblige removal of the discharge pipe from the well, the cost of the operation is considerable.
Submersible electric pumps are another popular means of pumping deep. These include multi-stage rotary turbine, eccentric piston and diaphragm types. These pumps employ rotary electric motors submerged with the related pumping means. They are generally slightly smaller than the inside diameter of a well casing and are installed in a casing by lowering the pump to below the static fluid level. The pump is powered by a high amperage electric supply cable and is installed with an independent discharge conduit as well as a safety cable. While low flow submersible DC electric pumps are now available which are quite energy efficient, they are limited to depths of less than 100 to 200 meters. Furthermore, they typically operate at very low discharge rates. AC electric deep well turbine pumps can lift water from depths of over 300 meters at a rapid discharge rate, but they typically operate at efficiencies well below 80%. In any case, a large diameter well bore must be drilled to eventually receive the down hole pump and motor, and a discharge conduit other than the casino is typically required.
The cost of casing is an important consideration in non-hard rock well construction. Small diameter casing may be safely employed at a greater depth than larger diameter casing having the same wall thickness, as it is more resistant to the lateral pressure from the surrounding strata. Accordingly, savings can be effected where casing size and related bore size can be minimized. Even in hard rock wells, and particularly where free flowing water or oil is known to be present, minimal bore diameter may be determined by the lateral space requirements of the pumping system to be installed.
A novel double acting reciprocating piston pump is disclosed by Ramsower, U.S. Pat. No. 5,058,667. This design appears to include most of the above mentioned drawbacks of single acting piston pumps as it requires a rigid discharge pipe and drive rod to secure and operate the pump within the well. Its double acting operation further requires a submerged down hole weight to return the plunger to the bottom of its stroke while simultaneously counterbalancing and lifting fluid up the discharge pipe to the well head. In deep wells, the size of the counterbalance would be very large of a necessity, and would require that the bore hole accommodate the counterweight protruding far below the pump. Hydraulic friction on the counterbalance would be considerable, especially in viscous fluids.
To overcome the deficiencies of the aforementioned technologies, the inventor sought to design a pump that could be remotely secured within a narrow diameter bore. While down hole anchoring systems are not in wide use today Wolf, U.S. Pat. No. 3,510,234 discloses a single acting cable operated pump utilizing a down hole locking mechanism which enables use of the casing as a discharge conduit. Wolf's design has several drawbacks, the most important being that the bulky locking mechanism significantly impedes potential flow through the juncture between the pump and the well casing. Further, the lock is activated by downward expansion of a resilient collar by a mandrel. This approach to installation obviates the possibility of pulling upward on the pump to expand the collar, as the pump cannot rise in the casing and frictionally communicate with the casing walls at the same time. In addition, it appears that it would be very difficult to free Wolf's collar from the casing walls after having been installed for a long period of time. Pulling upward on the pump would tend to exacerbate a stuck installation, even with the mandrel removed. This and other reasons may account for the fact that Wolf's design apparently has not been widely used.
Nixon and Park, U.S. Pat. No. 1,941,813 disclose a down hole anchor for tubing which is activated by downward fluid pressure on a bellows type collar. This installation is only for use with coaxial discharge tubing within the casing, and requires considerable amount of space to be effectively deployed. Linkous, U.S. Pat. No. 2,930,327 depicts a roller cam device for centering a discharge pipe in the well casing. Both of these systems demand a discharge pipe coaxial with the casing. Neither of these types of lock is used to seal the pump within the casing so that the casing may be employed as the discharge conduit. Hahs, U.S. Pat. No. 3,485,181 cites a support for a subterranean pump installation with an independent but related sealing means to use the casing as a discharge conduit. However, Hahs's lock and seal are designed to be used in conjunction with a rotary turbine pump and they are unnecessarily complex for many pump installations.
In view of the foregoing, existing pumping means available for confined tubular applications have a number of significant limitations. These include the requirement of large bore diameters relative to pump output capacity, low operating efficiencies at high discharge rates, the need in some applications for cumbersome and costly support and counterbalancing structures, and highly uneven power demand on the prime mover in single acting reciprocating pumps. In well applications, costly wide-bore casing) must be provided to receive down hole pumping means, the bore diameter often being considerably in excess of what would be required if smaller diameter, high production pumps were available. Much existing pump technology is capital intensive and in oil wells particularly, pumps in common use are costly to service and repair due to the weight of the drive rod and pipe string which must be removed to remove the barrel.